Pressure control apparatus for pressure cookers



Oct. 5, 1954 v sc E JR 2,691,090

PRESSURE CONTROL APPARATUS FOR PRESSURE COOKERS Filed June 21, 1949 5Sheets-Sheet l Oct. 5, 1954 I v sc g JR 2,691,090

' PRESSURE CONTROL APPARATUS FOR PRESSURE COOKERS Filed June 21, 1949 5Sheets-Sheet 2 START J52 J52 'c r va e Oct. 5, 1954 v sc JR 2,691,090

PRESSURE CONTROL APPARATUS FOR PRESSURE COOKERS wazyw/zab a JTZLAQJZMgag 1W7 nn fi Cider/y: 2

Patented Oct. 5, 1954 UNITED STA'lES PATENT OFFICE PRESSURE CONTROLAPPARATUS FOR PRESSURE COOKERS Gertrude V. Bouton Application June 21,1949, Serial No. 100,346

6 Claims.

My invention relates generally to pressure control apparatus, and moreparticularly to such apparatus for use in controlling and maintainingthe desired operating pressure in pressure cookers and canners.

In canning and preserving foods, especially in homes, one of the primaryproblems is the maintenance of a constant temperature throughout thesterilization or canning processes. Properly to sterilize foods forcanning, requires that the food be maintained at a certain temperaturefor a predetermined time interval. While these two factors may difierfor various foods, it is highly desirable that means he provided forcontrolling both factors accurately. The time factor may be controlledquite readily by a suitable time clock device, but in the past theperson attempting domestic canning did not have available means formaintaining the temperature constant for the desired process.

Most canners are equipped with means to prevent the pressure within thecanner from exceeding a predetermined value, such as 15 p. s. i. (gauge)or 10 p. i., but no means are provided to prevent the pressure fromdropping below the predetermined desired value, and thus, in endeavorsto maintain the proper pressure in the canner, it was necessary, at veryfrequent intervals, to adjust the device supplying heat to the canner,and even if the operator was meticulous in making such adjustments,substantial fluctuations in the pressure within the cooker were nearlyinevitable.

It will be understood that in pressure cooking operations, thetemperature of the steam surrounding the food is directly related to thepressure within the cooker, provided, of course, that the cooker notcontain air. Thus, for example, at a pressure of 15 p. s. i., saturatedsteam will have a temperature of 250 F., while at 10 p. s. i. thetemperature of saturated steam is 24i0 F. Furthermore, as the foodwithin the pressure cooker is raised in temperature, the rate at whichit is capable of absorbing heat diminishes to a certain extent,depending upon the character and amount of the food within the canner.Thus, even if the application of heat to the canner is at auniform rate,the pressure (and hence the temperature) within the canner intervalduring the canning will tend to rise, and the operator must accordinglyreduce the rate of application of heat to the canner.

Thus in domestic canners of the prior art, it was always necessary forthe housewife to maintain a close watch on the pressure indicator of thecanner, and to regulate the height of the gas flame or the current inputto the heating unit of an electric range at frequent intervals, in orderto maintain the pressure in the canner at, or reasonably close to, thedesired cooking pressure, usually 15 p. s. i. or 10 p. s. i.

In the past, it has been attempted to avoid such undesirablefluctuations in pressure in the canner by using an unnecessarily largequantity of water in the canner. Such excess water, due to its latentheat, served as a heat reservoir, ballast, or cushion, and to a certainextent alleviated the difficulty of wide fluctuations in pressure. Theuse of such excess water, however, was undesirable in that it greatlyincreased the time required to heat the water to the temperature of 250F. (or 15 p. s. i.), and correspondingly lengthened the time required tocool the canner and its contents from the desired canning temperature toa temperature slightly below 212 F., at which the pressure within thecanner dropped to atmospheric pressure. Therefore, the time cycle of thecanner was greatly lengthened.

Time cycle is used herein to mean the time required to complete onecycle of a canning operation. In normal canning operations, the timecycle starts as the canner is heated, until a surficient amount of thewater therein has been converted into steam and discharged through thevent for a sufiicient length of time to assure that all of the airinitially contained in the canner has been exhausted, The operator thencloses the vent, usually by a gravity operated vent valve. During theinitial portion of the time cycle, the water within the container(assuming that the canning is to be don at 15 p. s. i.), must first beheated to 250 F., meanwhile converting sufficient of the water intosteam to raise the pressure to 15: p. s. i. Thereafter the pressure ismaintained at 15 p. s. i. for a length of time determined by theparticular food being canned. The application of heat is thendiscontinued, and the pressure permitted to drop to atmospheric, due toradiation or other losses of heat from the canner. When the pressure hasdropped to atmospheric pressure, and the food has been re moved the timecycle is completed.

It will be clear from the foregoing that if excessive water is used inthe canner, the time cycle will be greatly lengthened due to theincreased time required to raise the canner and its contents to thedesired canning temperature, and to the increased length of timerequired for the canner and its contents to be cooled sufficiently thatthe pressure therein will drop to atmospheric pressure.

During the time that the pressure within the canner is being raised fromatmospheric to the canning pressure, and during the time that the canneris dropping from the canning pressure to atmospheric pressure, the foodwithin the canner is, of course, being subjected to temperatures above212 F., and to a certain extent chemical changes take place during theseperiods while the pressure is rising and falling.

In canning delicate foods, such as tomatoes and fruits, it is highlydesirable that the food have its temperature quickly raised to thedesired sterilization temperature, and then have its temperature quicklyreduced, so as to avoid excessive and destructive heating of the food.Such delicate foods, if subjected to a long time cycle (even though thelength of time at which the food is maintained at the high sterilizationtemperature is short) are subject to physical and possibly also chemicaldeterioration, and it is therefore very difficult properly to can suchfoods in a canner having a relatively long time cycle, as has beennecessary with domestic canners in the past.

The use of an excessive quantity of water in a canner is also ofdisadvantage, since the aggregate amount of heat required for thecanning operation is increased by the use of such excessive water.

It is therefore one of the primary objects of the invention to providean improved pressure canner or cooker in which a minimum amount of wateris required, and, as a consequence, in which the time cycle isrelatively short.

A further object is to provide an improved pressure canner or cooker inwhich the pressure may be maintained automatically at the requiredcanning pressure without attention on the part of the operator.

A further object is to provide an improved pressure control apparatusfor pressure canners and cookers, in which changes in calibration areeffected incident to each cycle of operation of the canner, so thatunavoidable variations in the operation of the various parts of thecontrol apparatus have no noticeable effect upon the operation of thecanner.

A further object is to provide an improved pressure control apparatushaving safety features, whereby misoperation is prevented or at leastindicated.

A further object is to provide an improved pressure control apparatusfor pressure cookers and canners, which is combined with the pressurecontainer by such means that there are no tubes, conduits, orpassageways which may become clogged, and thus interfere with the properoperation of the control apparatus.

A further object is to provide an improved pressure apparatus forpressure cookers and canners, which does not interfere in any way ormake more arduous the task of cleaning the pressure container.

A further object is to provide an improved pressure control apparatusfor pressure cookers and canners, which is operable to stop theapplication of heat to the container in the event that, throughinadvertence, an attempt is made to operate the canner without anadequate supply of water.

A further object is to provide an improved pressure control apparatusfor pressure cookers and canners, which will stop application of heat tothe container upon attainment of an excessively high pressure within thecontainer.

A further object is to provide a pressure control means for pressurecookers and canners, with improved means for indicating the condition ofthe heat applying means.

A further object is to provide an improved pressure cooker or cannerhaving an immersion type electrical heater, so incorporated in thecontainer that it may be easily cleaned and does not interfere with theplacing of the maximum quantity of containers or jars within the cooker.

A further object is to provide a pressure canner in which foods may becanned according to a fixed time table, with uniform results.

A further object is to provide an improved pressure canner havingcontrols incorporated therein for substantially reducing the time cycle,and thereby preventing the overcooking of foods, particularly suchdelicate foods as fruits and tomatoes.

A further object is to provide an improved pressure canner in which thepressure within the container may be maintained accurately within asmall range, in the order of one-quarter Other objects will becomeapparent from the following description, reference being had to theaccompanying drawings, in which Fig. l is a perspective view of apressure canner or cooker incorporating the invention;

Fig. 2 is a horizontal sectional view, taken on the line 22 of Fig. 1;

Fig. 3 is a vertical sectional view of the pressure operated switchmechanism, taken on the broken sectional line 33 of Fig. 1;

Fig. 4 is a sectional view, taken on the line 44 of Fig. 3;

Fig. 5 is a fragmentary sectional view showing particularly the latchand the bimetal latch releasing thermostat;

Fig. 6 is a fragmentary sectional view, taken on the line 65 of Fig. 5;

Fig. 7 is a fragmentary elevational view of the latch and associatedmechanism, the latch being broken away more clearly to show itsoperating spring;

Fig. 8 is a fragmentary sectional view, taken on a horizontal plane, andshowing the stuiiing box mounting of the immersion type electricalheating element; and

Fig. 9 is a partially schematic wiring diagram including some of theswitch actuating parts.

Referring to Fig. 1, the invention is illustrated as applied to apressure canner comp-rising a container 28, having an internally sealingcover 22, which is preferably of the type disclosed in my prior PatentNo. 2,282,011, the cover being warpable to a shape having an ellipticalprojection in a plane perpendicular to the polar axis thereof due tostresses within the cover, and being capable of being drawn into aconvex shape with its periphery in contact with the downwardly facingseating surface (in the form of a gasket) within the lip bead 24 of thecontainer,

such flexing of the cover being accomplished by a cam handle 26, whichwhen swung clockwise (Fig. 1) pulls the central portion of the cover '22upwardly by the action of the cam handle synthetic rubber plug 34operated as an over pressure or safety release plug in the event thatthe pressure within the container 22 greatly exceeds the normal cookingand canning pressures.

As best shown in Fig. 2, the canner is provided with an immersion typeelectrical heating unit 36, which is of arcuate shape extending throughabout 300 degrees, and which is nearly entirely contained within arolled reinforcing bead 38 formed in the bottom wall 46 of thecontainer.

This heatin unit is preferably of the Calrod type and has a cylindricalportion 42 which projects through a stufi box bushing 44 welded to thecylindrical wall 56 of the container 20.

As shown in Fig. 8, the stuiflng box bushing 44 is internally threadedto receive a packing nut at by which a suitable packing 56 may becompressed about the cylindrical portion 42 of the heating element andseal the joint against escape of steam. The packing is, however,sufficiently loose that the heating unit 36 may be swung upwardly aboutthe axis of the cylindrical portion i2 thereof so as to permit thoroughcleaning of the unit and of the inside of the bottom of the container26. The Calrod unit is provided with a pair of lead-in wires 52 and 53.

As shown in Fig. 3, the wall 46 of the container has near its bottom acircular opening 54 through which a pressure responsive plug 56 ispressed. When not subjected to pressure, this plug 56 assumessubstantially the shape in which it is shown in Fig. 9, but whensubjected to pressure the surface thereof within the container becomessubstantially flat, while the external surface thereof is bulgedoutwardly. The plug 56 is provided with an internal flange 58 and asmaller diameter external flange 66 so that it is self-retaining withinthe opening 54, and may be removed and inserted from the inside of thecontainer. It is made of a suitable elastic and resilient material suchas a synthetic rubber, preferably of the perbunan type, which isresistant to deterioration under the effect of oils and greases normallyencountered, and which is capable of maintaining its elastic propertiesthroughout the wide temperature range to which it is subjected, namelyfrom room temperature to approximately 250 F. The plug 56 operates as apressure responsive member to convert the pressure within the containerto a correspondin force for the operation of the control apparatus.

The control apparatus is mounted on a pair of generally U-shapedbrackets 62 and 64, the ends of the legs of which are welded to thecontainer wall 46. The control switch mechanism is mounted upon asubstantially rigid base plate ta, the lower end of which is rigidlysecured to the cross portion 68 of the bracket 64 by screws iii threadedin the plate 66 and holding the lower end of the latter spaced from thecross portion 68 by spacers 12.

While the plate 66 is relatively thick and thus quite rigid, it may beflexed slightly by means of a pair of oppositely acting adjustmentscrews l4 and 15, which are threaded respectively in the cross piece 16in the bracket 62 and in the base plate 66. It will be clear that byturnin the screw 74 inwardly, while unscrewing the screw it, the baseplate 66 may be flexed toward the plug 5t, and by turning the screws inreverse directions, th upper portion of the base plate as may be flexedaway from the plug 56, such adjustment being normally efiected onlyduring the assembly of the apparatus to allow for unavoidable variationsin the dimensions of the component parts. All of the control switchesare mounted on the base plate 66 so that their positions relative to theplug 58 may be adjusted by the screws l4 and i5 and locked in adjustedposition by these screws.

The switch assembly includes four flexible and resilient contact arms86, Si, 82, and 63, and supplementary leaf spring arms 84 and 85. Thelower of arms to are clamped to the base plate 65 by a pair of screws 86threaded in the plate 66, the screws being surrounded by insulatinsleeves 83 and 89, respectively, and all oi the switch arms except thearms 8i and 82, being insulated from one another by suitable insulatingplates 96, as is customary in switch i constructions of this type.

The upper end of the leaf spring at bears against the outer surface ofthe plug 56, and is provided to resist the initial bulging of thelatter. When the pressure within the container increases substantiallyabove atmospheric pressure, the upper end of the spring arm es engagesan insulating strip 64 which is eyeleted or otherwise suitably securedto switch arm 33. The switch arm 63 carries a round head contact rivet96 which is engageable with a flat surface contact rivet S8 secured toswitch arm During assembly of the apparatus, the initial position of theupper end of the switch arm 82 is determined by adjustment of a screwI00 which is threaded in a rigid metal strip 162 secured to the flexiblecontact arm 82 (preferably by welding) the end of the screw beingengageable with a rigid plate H14 mounted in the stack with theremaining contact arms and suitably insulated therefrom.

The strip IE2 has secured thereto an insulatll'lg pusher Hi6, which isgenerally cup-shaped in section, the left-hand end (Fig. 3) of thispusher being engageable with the contact arm 86.

The switch arm at is provided with a round head contact rivet Hi8adapted to engage a flat faced contact rivet HEB secured to the contactarm as. The contact arm 85 is held spaced from the slightly/flexiblestrip 65 by a cup-shaped insulating pusher H2 secured to the strip 85.The upper end of the strip 35 may be flexed toward and away from theplug 56 by rotation of a man-- ually operable knob lit which is securedto a tubular shaft H6 extending freely through protective casing i itwhich surrounds the switch mechanism. The inner end of the shaft HE hasa flange E26 which is held against the base plate $6 by a somewhatresilient perforated bracket H22 surrounding the shaft lit secured tothe base plate 656 by one or more screws [24. A cross pin or rivet we issecured to the tubular shaft H6 and extends diametrically thereof andthrough an elongated slot or lzerf lit formed in the end of an adjustingscrew 5323 which is threaded in the base plate st, and the inner end ofwhich engages the flexible strip 85.

The .fiange 520 of the tubular shaft I I6 lies adjacent a pin I32pressedin the base plate .66, and this .flange is of reduced diameterthroughout substantially 320 so as to leave a stop portion engageablewith the pin I32, limiting the rotation of the tubular shaft to an arcof somewhat less than 320. It will be clear from the foregoing that byrotation of the knob I I4, the screw iSll will operate to flex the'strip85 more or less, and through the insulating pusher II2 to move thecontact I58 toward or away from the contact IIG.

As best shown in Figs. 5, 6, and '7, a latch -I45) is pivotally securedto the upper end of the insulating strip at, having a portion extendingthrougha slot I42 formed in the strip 94, and having a portion I44 ofincreased width resting .in a groove I46 extending transversely of thestrip 94. The slot M2 is of sufiicient size that the latch I49 may swingfreely between its full and dotted line positions, as shown in Fig. 6.The latch 540 is substantially L-shaped in vertical cross section,having a downwardly extending portion I48 forming a sharp internalcorner M9 with respect to the main portion of the latch. This corner isadapted to engage over and latch against a wedge-shaped edge I50 formedat the upper end of the base plate 86.

The latch I lil is adapted to be moved from the position in which it isshown in dotted lines in Fig. 3, to its full line position, bydepression of a start button :52 carried at the upper end of a plungerIt, having a head I55 at its lower end, and suitably mounted forvertical sliding movement in the casing H8. The plunger I54 and startbutton I52 are arranged to be moved upwardly by a compression coilspring 58. The latch 45 is held in its unlatched position (the full lineposition in Fig. 6) by a wire spring I60 which is secured to theinsulating plate 94 by a hollow rivet I62, and the arcuately bent endsI64 of which project through a hole IE6 formed in the latch I44.

Secured to the upper end of the base plate 65 is an L-shaped bimetallicthermostatic element I53 which has an ear I55 extending sidewardlytherefrom and lying directly beneath the lat-ah I40 when the latter isin lateral position.

As will be apparent from, Fig. 7, the spring IE8 is biased to spreadapart, and the end portions IE4, by engaging the walls of the hole I65,exert a force on the latch which has an upward component and thus tendsto swing the latch I40 upwardly. The spring I60 also serves as a meansto hold the latch Mt assembled on the insulating plate 94.

The casing H8, as best shown in Fig. 1, encloses the operating parts ofthe control mechanism, being secured to brackets 62 and 54 by screws 151(Fig. 1), and has a pair of sockets I68 (Fig. 4) secured therein for thereception of lamps W and R, which are distinctively colored, as white(or clear) and red, respectively.

The casing H8 forms a support for plug connector prongs I12 which aresuitably insulated and are adapted detachably to engage in aconventional socket member H4 (Fig. l)- at the end of an extension cordH6 by which the apparatus may be plugged into a suitable electricalcurrent outlet socket, using a conventional two prong plug I'EB securedat the other end of the extension cord I36.

As best shown in Figs. 3 and 4., and as diagrammatically illustrated inFig. 9, the connection prong I13 has one of the leadin wires 52 8 of theheating elementet connected thereto, the other lead-in wire'53 beingsoldered to the lower endof the contact arm 83.

The lamps W anclR, which are of the gaseous discharge type, areconnected in series across the connection prongs I12 and H3, and the twoseparate wires from these lamps are connected to lead-in wire .53, aswell as to the wire leading to switch arm 83, by a detachable thimbleI19, which is of insulating material and threaded over the twisted endsof these wires. The connection prong I12 is also connected to contactarm 80, and hence to contact rivet Ht. (For ease of understanding, themechanical relation of the parts shown in Fig. 9 is not exactly the sameas in the structural figures, but the principle of operation isidenticalin all the figures.) With the parts, particularly the rubberplug 5% and the strip '94, in the position in which they are shown inFig. '9, which is the position assumed when there is no pressure withinthe container and the start button I52 has not been operated, the leafspring 84 presses against the outer surface of the plug55 to provide aninitial restraining force and to assist its internal elastic forces inaiding restoration to "its normal position, and the con- "tacts 96 and98 'are separated by virtue of the initial bias given to the contact arm83, which carries the contact rivet '95.

When it is desired to utilize the cooker in the performance of a canningoperation, a limited amount of water is placed in the container and thecans or jars filled with food to be sterilized or preserved are placedin the container, being supported therein by a rack of customaryconstruction. Thereafter the cover 22 is inserted and flexed to sealingposition by means of the cam lever .26 so that the cover engages theseal within the head 24 of the container 26. The vent valve is removedand the connection plug I18 connected to a line socket. The operator.then depresses the start button I52, .causing the latch I .to swingfrom the position in which it is shown in 'dottedflines in Fig. 3, tothe position in which .it is shown in full lines in said figure, suchmovement of the latch being effected against the very slight restrainingforce applied by the spring I60.

As the latch I49 swings downwardly, its downwardly .bent portion I48engages the wedge-edge I of the base plate .65, and the latch M0 thusexerts a leftward pull upon the insulating strip 94, moving the lattersufiiciently to cause electrical contacting engagement of the contactrivet 96 with its complementary contact rivet =98. When the latch isswung downwardly to its full extent, the wedge shaped edge I58 of the.base plateBS engages in the sharp corner I49,

.making .substantially line contact therewith.

Since atthis time there is no superatmospheric pressure within thecontainer, the switch IEiB-I Ill will be closed and thus the closure ofswitch 96Qi3 will :complete the circuit to the electrical resistanceheating unit 36, and heat will be supplied to the water around the .im-.mersed heating element, raising the water to boiling temperature andevaporating sufficient water that the air initially trapped within thecontainer will be exhausted through the vent valve opening, whereuponthe operator, by noticing the emergence of steam from the port of thevent valve 30, will place the vent valve to the continued application ofheat by the heating element 36.

Referring to Fig. 9, it will be noted that when both switches 96-98 andHIS-i iii are closed, the junction between the lamps W and R is at thesame potential as connection prong 2'13. Thus the lamp W has nodifference in potential across its electrodes. However, under thesecircumstances, the lamp R is in parallel with the heating element 36 andeffectively connected across the connection prongs I12 and H3 so that itwill be illuminated.

As the steam pressure within the container rises and the plug 56 bulgesfarther outwardly, it will cause the leaf spring 84 to engage theinsulating strip 94 and swing the latter toward the left, thus freeingthe corner 149 of the latch I40 from engagement with the edge [58, andpermitting the spring Hill to snap the latch let upwardly to theposition in which it is shown in full lines in Fig. 6. At the time thisoccurs, the contact 96 will be held in engagement with contact 98 by thebulging plug 56, and thus the circuit to the heating element 36 willremain closed.

As the steam pressure rises further within the container, and it reachesthe desired sterilization or canning pressure temperature, this will beindicated by the pressure indicator 32 and also by the fact that steamwill commence escaping past the gravity vent valve to, causing thelatter to jiggle. Thus by sight and sound the operator is apprised thatthe required pressure temperature has been attained.

The knob H4 will usually be in such position that the switch l08ll0 isstill closed. The operator then grasps adjusting knob H l and turns thelatter clockwise, causing the screw I30 (through the intermediary ofstrip 85, pusher H2, and contact arm 8|), to move the contact rivet I08away from the contact Hit. As soon as the circuit through the heatingelement is thus broken by the opening of switch [M -I it, the white lampW Will be effectively in series with the heating element 36 across theconnection prongs I12 and I73, and the white lamp will be illuminatedbecause the voltage drop across resistance of the heating element 36 isnegligible under these circumstances. The red lamp R will not beilluminated since its termi-- nals are under these conditions atsubstantially the same potential.

As soon as the white lamp is illuminated, the operator will stoprotating the adjustment knob lid. Thereafter, due to radiation of heatand continued absorption of heat by food within the container, thepressure within the container will gradually drop, and the outward bulgeof the plug 56 will decrease slightly until the rightward swinging ofthe contact arms 82 and 33 in unison will, through the moving away ofthe pusher Hi6, permit the contact arm 80 to flex to the right, againclosing switch ll3-l Ill. The apparatus may readily be constructed on acommercial scale with commercial tolerances, so that this reclosing ofthe switch ifid-l Hi will occur after drop of less than .50 p. s. i. ascompared with the pressure in the container when this switch was openedby adjustment of the knob 1 Hi.

Whenever both switches 95-98 and tilt-4H3 are closed, the red lamp Rwill be illuminated, indicating to the user that current is beingapplied to the heating element 36, While when either of these switchesis open the white lamp W only will be illuminated, showing to the userthat the pressure within the container is being maintained and that linecurrent is still being supplied to the connection prongs H2, H3.

The opening and closing of the switch Wit-4 ill will occur at intervalsthroughout the period of sterilization or preservation desired for theparticular food in the container, and upon. expiration of this desiredperiod, the plug H8 or the socket I'M may be disconnected. ihe containerand its contents will then gradually cool down to 212 E, that is, thepressure within the container will drop to atmospheric pressure,whereupon the user by swinging the handle 26 counterclockwise (Fig. 1)may permit the cover 22 to assume its warped shape, whereupon it may bereadily removed from the container.

If the user of the apparatus inadvertently forgets to place water in thecontainer, and after sealing it presses the start button I52, theheating element will be supplied with current in the manner previouslyexplained. However, pressure will not build up in the container becauseof the lack of water therein, and the plug will remain in the shape inwhich it is shown in Fig. 9. However, heat from the heating unit it willrapidly raise the temperature of the container walls and this heat willbe conducted and radiated to the thermostatic bimetal I53, causing thelatter to flex upwardly, and through engagement of its ear I55 with thelatch Mil, swing the latter from engagement with the edge Hit.

It is because of the requirement or" a very high degree of sensitivityin the holding power of the latch 1%, that it is highly desirable thatthe engagement between these parts be by substantially line contact, andthat the lug of the base plate 60, which has the edge I59 thereon, bebent forwardly, as best shown in Fig. 6, so that as the latch releasesfrom contact with the edge I58, there will be no further contact of thelatch with any part of the base plate at, and the latch will thus snapto its upper position.

It will be understood that under the last assumed conditions, when thelatch is released by the overheated bimetal Hit, the spring arm 83 willflex to the right, the switch arm 82 being arrested when adjustmentscrew ills comes into contact with the fixed stop EM, and the switch96-418 will be opened, shutting off the supply of current to the heatingelement 35. The white lamp W will be illuminated so that by occasionalinspection under these very unusual circumstances, the operator will beapprised that the canner is not operating properly by virtue of the factthat the lamps W and R, do not blink in alternation.

Of course under the assumed condition, that of having started the heaterwithout any water in it, the operator would also be apprised of theerror by the fact that steam was not emitted during the period duringwhich it was endeavored to exhaust the air from the container. However,under somewhat similar conditions, if the user failed to place suficientwater in the container upon starting, or if an. excessive amount ofwater was permitted to escape as steam past the vent valve 3B, thethermostat bimetal i525 would also operate to open the circuit to theheating element and to cause steady illumination of the lamp W. Suchsteady illumination of the lamp W would constitute an indication thatthe canner was not operating properly.

From the foregoing, it will be seen that I have provided a pressurecanner and control apparatus therefor which will operate satisfactorilyunder :3. wide range of-normal and inadvertently abnormal conditions.Under normal conditions it will reduce fluctuations in pressure duringthe preserving or sterilizing period to a range of. less than .50 p. s.i. By thus greatly limiting the pressure: fluctuations, the canning timemay be very accurately determined to produce canned food of the mostdesirable physical and chemical characteristics, improving both thetaste and appearance. of most canned foods.

Furthermore, any so called leaking or boiling off of the fluid withinthe jars or cans believed by some to be due to sudden and wide rangefluctuations of the pressure within the container, is completelyavoided, or at least reduced to a negligible minimum.

The fact that the user in effect calibrates the control apparatus foreach canning cycle, by adjustment of the knob H4, makes it possible toconstruct the apparatus with parts made to large tolerances. Andfurthermore, compensation is made for any changes in most of the. parts,due to wear, warpage, temperature changes, etc., eachv time the pressurecanner is used, by the adjustment of the knob H4.

Since the lead-in wire 53 is joined to the. wire connected to thecontact arm 83, as well as to two of the wires leading from theterminals of the two lamps, by a single detachable thimble I19, it willbe clear (by reference to Figs. 3 and 4), that the casing H8 and allparts carried thereby may readily be detached from the container and.control switch assembly by removal of the screws I67 and by removing thethimble I19 to permit disconnectionv of the four wire ends which arenormally held together thereby. Because of this construction. thecontact and switch parts are mad readily accessible for servicing.

While in the foregoing description the inven tion has been described asapplied particularly to a pressure canner, it will be understood thatthe invention is applicable with equal or possibly greater advantages,in pressure cooking.

While I have shown and described a preferred embodiment of my invention,it will be apparent that numerous variations and modifications thereofmay be made without departing from the underlying principles of theinvention. I therefore desire, by the following claims, to includewithin the scope of the invention all such variations and modificationsby which substantially the results of my invention. may be obtainedthrough the use of substantially the same or equivalent means.

I claim:

1. In a pressure control apparatus for pressure I cookers and cannersheated by connection to a source of electrical energy, the combinationof a pressure container, an electrical heatingelement therefor,a-fiexible plug secured in a wallv of the container, a first switch andasecond switch connected in series with the heating'element and thesource of current, manually operable means for closing said first switchand including a latch for holding said first switch in closed position,and means operable by the bulging of said flexible plug upon theattainment of substantial pressure within the container to hold saidfirst switch closed and release said latch, and upon attainment of apredetermined higher pressure within the container to open said secondswitch, said means being operable upon a decrease in pressure below saidpredetermined value to close said second switch.

2. The combination set forth in claim 1, in which there is included athermostatic bimetal part operable to release: said latch when. thetemperature of the cooker becomes excessively'high.

3. The combination set forth in claim 1', in which the second switch isprovided with means manually operable while the container is underpressure to adjust it to open at apressure slightly lower than saidpredetermined higher pressure.

4.. The combination set forth in claim 1, in which the first switchincludes a flexible switch arm and adjustable stop to limit movement ofthe arm in the direction to which it moves to close the switch, wherebythe switch may be adjusted so that it will open when the pressure in thecontainer drops to a certain pressure.

5. Means for controlling the steam pressure in a container having. apressure indicator associated therewith, having water therein, and anelectrical heater for the water, comprising, a flexible pressureresponsive element forming part of ,the heater wall, and a switchmechanism mounted: on the outside wall of the container adjacent thepressure responsive element, said switch mechanism having a pair ofswitches connected in. series for controlling the supply of: electricalenergy to the heater, the first of said switches being normally open andthe second being normally closed, manually operable means including aholding latch for closing the first said switches, said switchescomprising pairs of leaf springs having their free ends substantiallyin: alignment with the flexible portion of the pressure responsiveelement with. the first switch closer to said element and adapted to beoperated directly thereby, resilient means to release said latch whensaid first switch has been enaged and slightly moved by the pressureresponsive element as a result of the presence of substantial steampressure within the container, means operated by the first switch uponcontinued movement thereof as a result of increas- ,ing pressure in thecontainer to open said sec- ,ond switch, and manually operable means toeffect calibration of the pressure at which said second switch is openedby said first switch.

6. Means for controlling the steam pressure in acontainer having watertherein and an elec- ,trical heater for the water, comprising, aflexible pressure responsive element forming part of the container wall,and a switch mechanism mounted on the outside wall of the containeradjacent the pressure responsive element, said switch mechanism having apair of switches connected in series for controlling. the supply ofelectrical energy to the heater, the first of said switches beingnormally open and the second being normally closed, springreturnedmanually operable means ,for closing the first said switches, alatch mechanically connected to a part of the first. switch to hold thelatter closed upon release of the manually operable means, said switchescomprising pairs of leaf springs having their free ends substantially inalignment with the flexible portion of the pressure responsive elementwith the first switch closer to said element and adapted to be operateddirectly thereby, resilient means to release said latch when said firstswitch has been engaged and moved by the. pressure responsive element toan extent. resultant from the presence of substantial steam pressurewithin the container, means operated by the first switch upon. continuedmovement thereof as a result of increasing pressure in the container toopen said second switch, and manually operable meansto 13 effectcalibration of the pressure at which said second switch is opened bysaid first switch.

References Cited in the file of this patent UNITED STATES PATENTS 5Number Name Date 1,014,450 Carlsson Jan. 9, 1912 1,387,686 Chase Aug.16, 1921 1,558,651 Thompson Oct. 27, 1925 10 2,269,689 Reichold Jan. 13,1942 2,274,930 Newton Mar. 3, 1942 Number 14 Name Date Myers July 14,1942 Stebbins Nov. 14, 1944 Allen Feb. 20, 1945 Newell June 24, 1947Graves July 22, 1947 Shields Jan. 6, 1948 Clark Apr. 20, 1948 Brown Nov.30, 1948 Lee Apr. 19, 1949 Whitney June 7, 1949

